1. Field of the Invention
The present invention relates generally to power distribution equipment and, more particularly, to a switchgear cabinet within which circuit breakers and the like can be disposed and that is configured to resist unintended opening in the event of an arc fault or other fault.
2. Description of the Related Art
Metal-clad switchgear is desirably employed for medium voltage switchgear operating at voltages from 5 to 38 KV, and for even higher voltages. The design of such metal-clad switchgear typically concentrates on structures that reduce the possibility of arcing faults within the enclosure. For instance, all primary elements such as breakers, voltage transformers, and control power transformers have disconnect means with isolating shutters to establish isolation from high voltage sources. All operations on breakers and the like disposed within metal-clad switchgear are preferably performed with the compartment doors closed for operator safety. The front door may be interlocked with the shutter assembly to reduce the chance of accidental opening of the front door during partial levering-in of the circuit breaker or other equipment.
The switchgear enclosures that contain the primary elements of the power distribution system such as the circuit breaker compartment, the main bus compartment, and the cable compartment have been compartmentalized and grounded for maximum isolation and confinement within these compartments, and all live parts where possible are fully isolated to reduce the likelihood of an arcing fault.
Although arcing faults are rare, injuries from arcing faults in metal-clad switchgear nevertheless may occur. Arcing faults are very destructive due to the high energy levels reach within the confined compartment. The structural containment must be adequate to substantially prevent the escape of arcing products and hot gases from the faulted compartment. Burns can result if operating personnel are in close proximity with the faulted switchgear.
Arcing faults can occur within a switchgear compartment as a result of insulation failure or human error. The pressure from an electric arc is developed from two sources: the expansion of the metal by boiling, and the heating of air by arc energy. Copper expands by a factor of 67,000 times in vaporizing. This accounts for the expulsion of near-vaporized droplets of molten metal from the arc. One test has shown that droplets could be propelled up to ten feet. The pressure also generates and directs plasma outward from the arc for distances proportional to the arc energy. One cubic inch of copper vaporizes into 1.44 cubic yards of vapor. The air in the arc stream expands due to its being heated from ambient temperature to the temperature of the arc (approximately 35,000xc2x0 F.).
All of this happens within the first half cycle of the fault and results in a sudden and dramatic increase in pressure within the compartment. Such elevated pressure acting on the door of the faulted compartment can potentially generate sufficient force to blow the door off the cabinet. Switchgear cabinetry thus must be designed not only to reduce the likelihood of arcing but also to contain and withstand the pressures that are created during such arcing in order to prevent personal injury.
Switchgear can be designed in numerous ways to retain the door thereon and to resist the door from being blown open or off during an arcing fault. Some such doors have included overlapping or interlocking members around the perimeter of the door that operate as interference structures that interfere with movement of the door away from the frame of the switchgear cabinet and thus help to secure the door to the frame.
In one type of switchgear cabinet, it has been known to provide a locking mechanism on a door of a cabinet that includes a plurality of latches that are simultaneously operated by an operating rod connected with a handle. The latches each include a pin, and the pins are selectively engaged with holes formed in plates that are bolted or otherwise mounted to a vertical frame member of the switchgear cabinet. Such plates have, however, previously been configured to each include a bend that defines a protruding lug within which the hole is formed. Such a configuration is necessitated by the desire to simultaneously operate the latches to allow simultaneous engagement of the pins in the holes. A noted shortcoming with such a configuration has been that the plates have tended to fail by catastrophic rupture at the bend in the event of an arc fault or other fault. It thus is desired to provide an improved switchgear cabinet that permits the use of a plurality of vertically spaced latches on a door that are simultaneously operated with an operating rod, but in which the plates with which the pins of the latches are engaged are not formed with a bend and thus are relatively more resistant to catastrophic failure in the event of an arcing fault or other fault.
In view of the foregoing, a switchgear cabinet includes a plurality of securing apparatuses that are mounted on a vertical flange of the switchgear cabinet, with the securing apparatuses each being formed with a locking hole that is engageable by a pin of a locking mechanism on a door member. Each securing apparatus includes an anchor plate connected with a first bracket and a second bracket, with the first and second brackets being mounted on the flange of the switchgear cabinet. The locking hole is formed in the anchor plate, and the anchor plate is substantially planar and free of bends. The anchor plate further is generally U-shaped and is configured to extend generally around at least a portion of the flange.
An aspect of the present invention is to provide an improved securing apparatus for a switchgear cabinet in which the securing apparatus is more resistant to catastrophic failure in the event of an arcing fault than previously known securing structures.
Another aspect of the present invention is to provide a securing apparatus for a switchgear cabinet in which the securing apparatus includes an anchor plate that is substantially planar and free of bends.
Another aspect of the present invention is to provide an improved securing apparatus for a switchgear cabinet that is co-operable with a locking mechanism mounted on a door member of the switchgear cabinet, with the locking mechanism being of a type that includes a plurality of vertically spaced latches that are simultaneously operated by a common operating rod.
Another aspect of the present invention is to provide a securing apparatus for a switchgear cabinet, in which the securing apparatus includes an anchor plate that is of a generally U-shaped configuration and that extends generally around at least a portion of a flange of the switchgear cabinet.
Accordingly, an aspect of the present invention is to provide a securing apparatus for use in a switchgear cabinet, the switchgear cabinet including a case and a pin, in which the general nature of the securing apparatus can be generally stated as including an anchor plate formed with a slot and a locking hole, the slot being structured to receive at least a portion of the case therein, the locking hole being structured to receive at least a portion of the pin therein, and a support connected with the anchor plate and structured to be mounted on a portion of the case.
The support may include a first bracket and a second bracket. The first and second brackets may be disposed on opposite sides of the slot, and the first and second brackets may each include a flange plate, with the flange plates being oriented substantially parallel with one another and being structured to receive the flange therebetween.
The anchor plate may include a base plate, a first tab, and a second tab, with the first and second tabs extending from the base plate and being disposed on opposite sides of the slot, and with the base plate and the first and second tabs together being of a generally U-shaped configuration. The locking hole may be formed in the first tab, and the base plate and first tab may be substantially free of bends.
Another aspect of the present invention is to provide a switchgear cabinet, the general nature of which can be stated as including a case, a door that is movable with respect to the case, and at least a first securing apparatus, the at least first securing apparatus being disposed on a portion of the case, the door including at least a first pin, the at least first securing apparatus including an anchor plate and a support, the anchor plate being formed with a slot and a locking hole, the portion of the case being received in the slot, and at least a portion of the at least first pin being receivable in the locking hole, the at least first securing apparatus being structured to resist movement of the door with respect to the case when at least a portion of the at least first pin is received in the locking hole, and the support being connected with the anchor plate and being mounted on the portion of the case. The securing apparatus may include additional features as set forth in the paragraphs above.